The major source of food for humans and for animals is cereal grains. The production of cereal grains per acre has been increasing rapidly. Harvesting, handling and drying of grains have become necessary for economically preserving the crop produced, along with the increase in yield. Various methods for preserving the crops are available. Moisture is removed to prevent development of a favorable environment for growth of molds and insects that normally cause spoilage. In this paper, a grain drying model has been proposed. Thin layer semi-empirical equations have been used for predicting the air humidity, air temperature and grain temperature with variation of height of a fixed bed of grains in the unsteady state. Effects of variation of air velocity and voidage have also been incorporated. The coupled equations, partial and ordinary, have been solved by using a backward implicit numerical scheme and Runge–Kutta method.